ALPHA-GLYCOPYRANOSYL AND BETA-GLYCOPYRANOSYL PHOSPHATES AND 1,2-PHOSPHATES - ASSIGNMENTS OF CONFORMATIONS IN SOLUTION BY C-13 AND H-1 NMR

The 'H and 13C NMR parameters of the anomeric pairs of aldopyranosyl phosphates and their rigid 1,2-phosphate derivatives are reported. The derivatives of d-glucose, d-galactose, and d-mannose exist in the 4C1 conformation while the l-fuco derivatives are in the 1C4 conformation. As judged by 31P-1H and 31P-13C coupling constants, all of the a anomers of the aldopyranosyl phosphates have the phosphate moiety predominantly trans to C(2) while in the β anomers other rotamers make significant contributions. This relationship remains the same for the biologically important nucleoside diphosphate sugars (UDPGlc, UDPGal, GDPMan, and GDPFuc). From the pH dependence of l3C chemical shifts, observed in 0.5 M solutions, the pK a2 of the a anomers is 6.1 while the pK'a2 of the βanomers is 0.6-0.8 pH unit lower. In the 1,2-phosphates, the chair conformation of the parent aldose is retained while an envelope conformation is formed by the cyclic phosphate. In the a anomers, the plane is formed between C(2), C(l), O(1), and P while O(2) is above the plane. In the β anomers, O(l) is out of the plane formed by the other atoms. The β anomers have phosphorus coupled to C(3) with coupling constants of 10.8-11.7 Hz, approximately 2 Hz greater than the maximum reported for trans coupling (Lapper, R. D., & Smith, I. C. P. (1973) J. Am. Chem. Soc. 95, 2880). © 1979, American Chemical Society. All rights reserved.